How the eye works

The muscles that control the pupil are found in the iris, that’s the coloured part of the eye surrounding the pupil. You probably think of yourself as having blue or green or brown eyes, but in fact you’re far more unique than that. That’s because each iris has a pattern of ridges and folds that are specific to you.

The pupil is a smart fellow, helping you see more when it gets dark. In low light, the pupil dilates. This allows more light to pass through the eye, giving you a better idea of what’s going on.

Waves of light bounce off whatever you’re looking at and enter your eye through the cornea. Once light passes through the cornea, it has to go through the pupil – that’s the little black dot at the centre.

This bit is important, so focus. The flexible lens that sits behind the iris changes its shape to allow you to see clearly. It flattens so you can see things at a distance and, when you look at something up close, it becomes thicker. This focuses light waves on their target – the retina at the back of your eye.

The ciliary body is part of the eye located behind the iris. It plays an important role in vision by having dual functions; it produces aqueous humour and is involved in adjusting the shape of the lens. 

The sclera is the white layer of the eye that covers most of the eyeball. It is made of tough, fibrous tissue and is known as the protective layer of the eye — continuous with the cornea.

The choroid is a thin layer of tissues between the sclera and retina. It serves as a vascular platform, delivering nutrients and oxygen to the layer of cells located at the back of the eye, known as the retinal pigment epithelium (RPE) and the outer nuclear layer of the retina.

The macula is located at the centre of the retina, at the back of the eye. It is the part of the eye that processes what you can see directly in front of you, otherwise known as your central vision.

Cones and rods are the photoreceptor new cells found in the macula — in the centre of the macula, known as the fovea. These are cells that generate a neural impulse when stimulated by light which passes to the brain and creates vision, enabling people to see fine detail and colour. 

The retina consists of millions of light sensitive rods and cones. They convert light waves into electrical signals that pass through the optic nerve. Your eye has three different types of cones, allowing you to see different colours. Rods are more sensitive than cones, but they can’t detect colour. That’s why colours are hard to see when the light is low.

The optic nerve is like cable TV for your head. It transmits electrical signals created by the millions of rods and cones on the surface of your retina. Your brain then interprets these signals as the object you see in front of you.

This is a thin, watery fluid produced by the eye, helping the cycle of production and drainage. The aqueous humour is 99.9% water and 0.1% nutrients such as glucose, proteins and vitamins. These nutrients nourish the cornea and lens and keep the eye healthy, as well as protect the cornea against wind, pollen, dust, and pathogens. 

The fluid fills the spaces between the cornea and iris, and the iris and lens, which gives the eye its round shape and controls intraocular pressure (IOP). It’s secreted by a structure called the ciliary body which is an extension of the iris (the coloured portion of the eye).

The highway to the retina is made up of vitreous humour, a kind of gel that consists of 99% water and fills your eye, maintaining its shape, like air in a beach ball. Although of course your eye is only about an inch in diameter, making it a little bit smaller than a squash ball.